California’s expert witness disclosure rules, set out in Code of Civil Procedure sections 2034.210 through 2034.730, let any party in a civil case force a mutual, simultaneous exchange of expert information before trial. Once a party serves the written demand, both sides face firm deadlines to identify their experts, produce supporting documents, and make those experts available for deposition. Miss a step and the court can bar your expert from testifying.
How the Demand Starts the Clock
The process begins when any party serves a written demand for exchange of expert witness information. No court permission is required. The demand must be served by the 10th day after the initial trial date is set, or 70 days before that trial date, whichever is closer to trial.1California Legislative Information. California Code CCP 2034.220 – Demand for Exchange of Expert Witness Information When trial is set well in advance, the 70-day mark usually controls.
The demand itself specifies the exchange date. That date must be 50 days before the initial trial date, or 20 days after service of the demand, whichever is closer to trial.2California Legislative Information. California Code CCP 2034.230 Either side may move for a different exchange date on a showing of good cause. The windows are tight on purpose: they leave room for depositions of the disclosed experts before discovery closes.
What You Have to Disclose
The heart of the exchange is a written list of every person whose expert opinion you plan to offer at trial, with names and addresses. That list covers both retained experts hired for the litigation and non-retained experts such as treating physicians who were involved in the underlying events.3California Legislative Information. California Code CCP 2034.210 – Exchange of Expert Witness Information If you do not intend to call any experts, you still have to say so in writing.4California Legislative Information. California Code CCP 2034.260
Retained experts trigger more. Any expert who is a party, employed by a party, or hired specifically to form opinions for the case must be accompanied by an expert witness declaration signed by the attorney under penalty of perjury. It has to contain five things:
- A brief narrative of the expert’s qualifications.
- A brief narrative of the general substance of the testimony the expert is expected to give.
- A representation that the expert has agreed to testify at trial.
- A representation that the expert will be sufficiently familiar with the pending action to submit to a meaningful oral deposition on the specific testimony expected.
- The expert’s hourly and daily fees for both deposition and consultation with the retaining attorney.
Non-retained experts appear on the list by name and address only. No declaration is required for them, but the distinction matters: omitting the declaration for a retained expert is an independent basis for excluding that testimony.
The fourth element is the one that trips people up. Signing the declaration means representing that your expert is ready now to sit for a deposition and discuss the opinions in detail. If the expert has not actually reviewed the file, the deposition will show it.
Reports and Writings
The demand can also request all discoverable reports and writings prepared by retained experts in the course of forming their opinions. When that request is made, every party must produce those documents at the same time and place as the expert list and declarations.5California Public Law. California Code CCP 2034.270 Draft reports, written analyses, and notes tied to opinion development typically fall within this. A perfect designation still fails if the writings are withheld, because non-production is a separate ground for exclusion.
The Simultaneous Exchange
Neither side sees the other’s list first. All appearing parties exchange their expert information in writing on or before the specified exchange date, either at a meeting of counsel or by any service method allowed under CCP sections 1011 or 1013.4California Legislative Information. California Code CCP 2034.260 These disclosures go to the other parties, not to the court clerk. Keep a proof of service; if compliance is later disputed, that document does the work.
Adding Experts After the Exchange
Two different mechanisms cover post-exchange additions, and they answer different problems.
Supplemental Designation
If the opposing side designates an expert on a subject you had not planned to cover, CCP 2034.280 lets you supplement. Within 20 days after the initial exchange, you may add experts to address subjects covered by the other side’s designated experts, but only if you had not previously retained an expert on that same subject.6California Legislative Information. California Code CCP 2034.280 The supplemental list must include a declaration and any discoverable reports and writings from the added experts, and you must make them available for deposition immediately, even if discovery has otherwise closed. This is not a second look at your own case; it exists to answer a subject you hadn’t anticipated.
Motion to Augment or Amend
If you want to add a newly retained expert or change the substance of an existing expert’s expected testimony, you need a motion under CCP 2034.610.7California Legislative Information. California Code CCP 2034.610 Only parties who participated in the original timely exchange can bring it. The motion must be filed early enough before the discovery cutoff to permit a deposition of the new or amended expert, and it must include a meet-and-confer declaration.
To grant the motion, the court must find the opposing party will not be prejudiced and must consider the extent of their reliance on the original list. The court must also find either that reasonable diligence would not have produced the expert earlier, or that the omission was due to mistake or excusable neglect and the moving party acted promptly on discovering it.8Justia. California Code CCP 2034.620 – Conditions for Granting Motion to Augment or Amend Even if granted, the court typically conditions leave on immediate availability for deposition and may add terms such as a trial continuance or costs.
Who Pays the Expert for a Deposition
The party noticing the deposition of an opposing expert pays that expert’s reasonable and customary hourly or daily fee. The clock runs from the noticed start time (or the expert’s arrival, if late) until the expert is dismissed, whether or not a single question was asked.9California Legislative Information. California Code CCP 2034.430 A daily fee only applies when the expert attends for a full day or was required to hold the whole day open and canceled other commitments.
If counsel for the expert or a non-noticing party shows up late, that attorney personally pays the expert’s fee for the delay, capped at the fee the retaining party pays.9California Legislative Information. California Code CCP 2034.430
When Testimony Gets Excluded
If you unreasonably fail to comply, the court must exclude your expert’s testimony on objection by a party that made full and timely compliance. CCP 2034.300 lists four failures that trigger exclusion:10California Legislative Information. California Code CCP 2034.300
- The witness did not appear on the party’s expert designation.
- A retained expert lacked the required declaration.
- Discoverable reports and writings prepared by the expert were not produced when demanded.
- The expert was not made available for deposition.
Two things shape how the rule plays out. The statute uses “unreasonably failed,” which leaves the court some discretion to weigh the circumstances; a minor inadvertent omission promptly corrected reads differently from a deliberate refusal. And only a party who made its own complete and timely disclosure can invoke exclusion, so a party that missed its own deadlines cannot wield the other side’s slip as a sword.
Fixing a Missed Deadline
Missing the exchange entirely is not necessarily the end. CCP 2034.710 permits a motion for leave to submit expert information late.11California Legislative Information. California Code CCP 2034.710 It must be filed early enough before the discovery cutoff to permit depositions and must include a meet-and-confer declaration; exceptional circumstances may justify a later filing.
The bar for relief is high. The court must find all of the following:12California Legislative Information. California Code CCP 2034.720
- The opposing party will not be prejudiced in presenting its case on the merits.
- The failure resulted from mistake, inadvertence, surprise, or excusable neglect.
- The moving party sought leave promptly after discovering the error and served the proposed expert information on all other parties without delay.
When relief is granted, the order is conditioned on making the expert immediately available for deposition. The court may also permit the opposing side to designate additional experts, continue trial, or award costs. Courts read “excusable neglect” seriously. A party that simply forgot the deadline has a much harder path than one whose new counsel discovered the gap on inheriting the file.